> "After measuring a 4.9 magnitude seismic event tonight, South Korea’s defence ministry confirmed that it was caused by an underground nuclear test. North Korea’s nuclear capability is estimated to be about 2 kilotons."
I'm not sure if this source is confirmed or not, but very interesting...
For point of reference, Little Boy (the bomb dropped on Hiroshima) was 16 kilotons and 90k+ people. I'm sure there are a ton of other factors besides kilotons that determine how destructive the bomb is, but it's a data point to understand the potential magnitude.
This is their third nuclear test and every single one has failed to cross the eight kiloton boundary at least. If this one is a plutonium weapon like the others it suggests that they are having major issues designing or fabricating the implosion lens around the nuclear material. It is quite striking that they keep conducting tests and reducing their usable nuclear stockpile further. It is almost like they don't have the capability to get a reliable warhead.
Tests are typically conducted in vertical shafts, according to the Preparatory Commission for the Comprehensive Nuclear-Test-Ban Treaty (CTBTO). Holes are cut 1 to 3 meters wide and up to a kilometer deep. The atomic devices are assembled on site and placed in the hole, usually accompanied by lead-protected diagnostic canister that contains sensors to record the explosion. The tunnel is then filled with layers of pea gravel, sand and other materials to prevent radioactive material from being released into the atmosphere.
During a test, the explosion energy is released in less than a millionth of a second, according to CTBTO. The temperature will reach about a million degrees within a few microseconds, and shockwaves from the blast, depending on the size, can be detected by seismographs around the planet.
As you keep zooming out[1] of the location of this nuke, till you see atleast a whole portion of the earth, you will realize that the existence of this nuke (or the concept of where/how it will be used) is unnecessary.
I think the name of that road could be user supplied data to Google through that collaborative mapping effort in North Korea. I could be wrong, though.
My old geology teacher said that the test-ban-treaty was a huge boon to geologists, since there was now a bottomless pit of money to be used to build seismographs anywhere you wanted to build them.
An exploding buried nuke will send energy in all directions, thus the first movement of the ground is away from the epicenter for all measurement stations around.
An earthquake usually comes about because tension between different areas release, and in that case one part of the ground will start their movement away from the epicenter, the other part will start into the direction of the epicenter.
However, one might need measurement stations covering the whole globe to detect it this way.
edit: Hm, I can't find the image that I've seen in a plate tectonics book a year ago, but here's a plot from a model:
http://www.wlandry.net/Projects/Gamra
If you look at the arrows in light blue, you can see that some point into the direction of the epicenter while some point away, thus it's an earthquake and not a nuke.
